This invention relates to a blowdown grease fitting, and more particularly, to an improved blowdown fitting having a longer seal life and one adapted for use in applications where a lubricant and polyester plasticizer are injected through the fitting.
Blowdown type grease fittings are commonly used in large lubricant supply systems, and are generally intended to retain lubricant under high pressure within the system. Blowdown fittings typically include a plurality of sealing means, which enables high pressure within the body of the fitting to be bled off before injecting additional lubricant through the valve. A typical blowdown fitting is described, for example, in U.S. Pat. No. 3,605,948 to R. O. Wynn.
Prior art blowdown fittings have several substantial drawbacks. First, the primary sealing member is typically secured to a first body portion which, in turn, is threaded to a second body portion containing a primary sealing seat. Thus, the sealing member is rotated with respect to a seat as the seal is formed. It has been found that seals within such blowdown fittings may experience a short life before the seal starts to leak.
The reason for such poor life in prior art blowdown fitting seals is not entirely clear. It is believed, however, that seal life is detrimentally affected since the conical-shaped primary sealing member is fixed relative to the upper body of the fitting. As the seal is being made up by threading the upper body to the main body, any eccentricity of the conical-shaped member relative to the seat can cause galling of the sealing member or the seat. Also, the annular position of the sealing member with respect to the seat is fixed when in the sealed condition, so that any wear points on the surface of the sealing member or the seat will be in the same position althought the seal is repeatedly opened and reclosed.
Prior art blowdown fittings are difficult to manufacture and expensive to repair. A primary sealing member is typically provided on an elongated stinger assembly which is part of the upper body. If the primary sealing member corrodes or otherwise must be replaced, a new stinger assembly and upper body must generally be replaced. Moreover, manufacture of the upper body and an integral stinger assembly is difficult and time-consuming.
A further problem with prior art blowdown fittings is that a poor seal may occur between the fitting and the female portion of the device to be lubricated. A cone member may be provided in the fitting for engagement with the female portion of the device to be lubricated, but galling of the cone member may occur as the blowdown fitting is threaded to the device.
Another problem with conventional grease fittings is that they frequently rupture when a grease/polyester mixture is passed through the fitting. In recent years, it has become common to use grease not only for a lubricant, but also as a carrier of plastic particles designed to act as a sealer or a packing material. The packing material, such as Teflon.TM. or graphite impregnated asbestos, acts to some extent as a lubricant, but is principally intended to seal that area and make up dimensional variations between the rotational and stationary members of the general assembly being lubricated. Since the packing material may tend to disintegrate during continued operations, it has been found necessary to repack pumps and valves on a regular basis. Rather than dismembering the assembly for repacking, it has been found acceptable in many applications to inject grease and a packing-type material to the desired area. Regular injection of the grease/packing material composition replenishes the packing in the assembly and offers an efficient technique for substantially reducing both equipment down time and maintenance costs.
Some commercial high pressure grease fittings have a metallic ball which is acted upon by a spring and normally engages a seat to seal the grease within the fitting and the mechanical assembly. When a grease gun is attached to the fitting, the pressure of the injected grease unseats the ball and allows grease to enter the fitting and a passageway from the fitting to the desired place within the assembly. Movement of the ball away from the seat typically compresses the spring, and grease is allowed to flow between the ball and the internal walls of the fitting.
A problem has repeatably been encountered with the use of conventional grease fittings and grease/packing material mixtures. The packing material particles may become lodged between the ball and the internal wall of the fitting, so that the fitting becomes "plugged" and further passage of the mixture is not possible. When a fitting becomes plugged, the pressure from the gun is often increased in an attempt to "clear" the fitting. The pressure within the fitting is often increased, however, to the extent that the fitting "blows out". During blowout of the fitting, the high pressure buildup in the fitting causes a spring retainer to give way, so that the ball and spring can be expelled from the fitting.
The possible detrimental effects of a plugged or blown-out fitting are numerous. Additional lubricant may not be injected through a plugged fitting, so that the packing may deteriorate, causing a leak. Alternatively, the surfaces in the area of the packing may become scoured or otherwise damaged because the packing is not being replaced. If the fitting blows out, the ball may not seat to hold the lubricant in the assembly. More serious, however, is the possibility that the spring, ball, or other portions of the fitting may be forced into the area of the packing and damage the equipment intended to be lubricated.
The disadvantages of the prior art are overcome by the present invention, however, and an improved grease fitting is hereinafter provided.